Image-taking apparatus and focusing method

ABSTRACT

An image-taking apparatus is disclosed, which is capable of reducing the influence of the one-side blur by the automatic focusing function. The image-taking apparatus comprises a focus detector, which detects the focus state of the plurality of focus detection areas, and a selector, which selects a focus target area from a plurality of focus detection area based on the detection result of the focus detector. In a case where a first object distance to a first object is longer than a first predetermined distances and a second object distance to a second object, which exists on an outer side of the first object in the image-taking screen, is shorter than the first object distance by a second predetermined distance or more, the selector selects the focus detection area corresponding to the second object as the focus target area.

FIELD OF THE INVENTION

The present invention relates to an image-taking apparatus capable ofcontrolling focusing for a selected focus detection area of a pluralityof focus detection areas.

BACKGROUND OF THE INVENTION

The improvement of image quality by the elevation of an automaticfocusing function is increasingly required along with the popularizationof digital cameras in recent years. The conventional AF apparatusesgenerally use the contrast detection method for focusing in which afocus lens position where the maximum value of the high frequencycomponent in the luminance signal of an object image formed on animage-pickup element is obtained is determined as an in-focus position.

In addition, a camera is known, which has a plurality of focus detectionareas in its image-taking screen and performs focusing for theclosest-object-distance area of a plurality of focusable focus detectionareas so that focusing on an object existing in an area other than thecentral area in the image-taking screen can be performed.

However, the inclination or center misalignment between the image-takinglens and the image-pickup element, or the inclination of lens unitsconstituting the image-taking lens, which is caused by manufacturingerror, deteriorates the accuracy of focus detection. Further, theautomatic focusing on the basis of focus detection information with lowaccuracy causes a so-called one-side blur. The one-side blur means astate in which one side portion of the image-taking screen is in anin-focus state but the opposite side portion or the central portionthereof is in an out-of-focus state.

For solving the problems, a camera has been disclosed in Japanese PatentLaid-Open Application No. 2003-222787, in which the differenceinformation between the object distances of the in-focus focus detectionareas (hereinafter, it is referred to as an in-focus distance) iscompared with a reference difference, and the focus control is changedaccording to whether the difference information is larger than thereference difference or not. According to Japanese Patent Laid-OpenApplication No. 2003-222787, to reduce the one-side blur, focusing onthe central focus detection area is performed if the in-focus distancesof the focus detection areas are the same.

However, the camera disclosed in Japanese Patent Laid-Open ApplicationNo. 2003-222787 has problems that it is difficult to obtain an in-focusstate to an object in an area other than the central focus detectionarea, and it is difficult to obtain a best in-focus state to the samedistance objects though a large blur does not occur.

For example, in a scene shown in FIG. 7, the focusing on a floor lamp Sbehind a table T located in the central area of the image-taking screenis performed if the in-focus distance difference between two persons P1and P2 located on either side of the table T and the lamp S is less thana predetermined difference.

BRIEF SUMMARY OF THE INVENTION

One object of the present invention is to provide an image-takingapparatus and a focusing method capable of reducing the influence of theone-side blur by an excellent automatic focusing function.

According to an aspect, the present invention provides an image-takingapparatus that comprises: a focus detector, which detects the focusstates at a plurality of focus detection areas provided in animage-taking screen; and a selector, which selects a focus target areafrom the plurality of focus detection areas based on the detectionresult of the focus detector, an image-taking lens being focused on anobject in the focus target area. In a case where a first object distanceto a first object is longer than a first predetermined distance, and asecond object distance to a second object, which exists on an outer sideof the first object in the image-taking screen, is shorter than thefirst object distance by a second predetermined distance or more, theselector selects the focus detection area corresponding to the secondobject as the focus target area.

According to another aspect, the present invention provides animage-taking apparatus that comprises: a focus detector, which detectsthe focus states at a plurality of image areas provided in animage-taking screen; and a selector, which selects a focus target areafrom the plurality of image areas based on the detection result of thefocus detector, an image-taking lens being focused on an object in thefocus target area. In a case where a first object distance to a firstobject displayed in a first screen area of an image-taking screen islonger than a first predetermined distance, and a second object distanceto a second object displayed in a second screen area on an outer side ofthe first object in the image-taking screen, is shorter than the firstobject distance by a second predetermined distance or more, the selectorselects the image area corresponding to the second object as the focustarget area.

According to another aspect, the present invention provides a focusdetection method comprising: a focus detection step of detecting thefocus states at a plurality of focus detection areas provided in animage-taking screen; and a selection step of selecting a focus targetarea from the plurality of focus detection areas based on the detectionresult of the focus detection step, an image-taking lens being focusedon an object in the focus target area. In the selection step, in a casewhere a first object distance to a first object is longer than a firstpredetermined distance, and a second object distance to a second object,which exists on an outer side of the first object in the image-takingscreen, is shorter than the first object distance by a secondpredetermined distance or more, the focus detection area correspondingto the second object is selected as the focus target area.

According to another aspect, the present invention provides animage-taking apparatus that comprises: a focus detection step ofdetecting the focus states at a plurality of image areas provided in animage-taking screen; and a selection step of selecting a focus targetarea from the plurality of image areas based on the detection result ofthe focus detection step, an image-taking lens being focused on anobject in the focus target area. In the selection step, in a case wherea first object distance to a first object displayed in a first screenarea of an image-taking screen is longer than a first predetermineddistance, and a second object distance to a second object displayed in asecond screen area on an outer side of the first object in theimage-taking screen, is shorter than the first object distance by asecond predetermined distance or more, the image area corresponding tothe second object is selected as the focus target area.

Other objects and features of the present invention will become readilyapparent from the following description of the preferred embodimentswith reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing the structure of the digital cameraof an embodiment of the present invention.

FIG. 1B is a schematic view showing a focus detection area of thedigital camera shown in FIG. 1A.

FIG. 2 shows a flowchart of the operation of the digital camera shown inFIG. 1A.

FIG. 3 shows a subroutine's flowchart of the zoom operation shown inFIG. 2.

FIGS. 4A and 4B show a subroutine's flowchart of the image-takingoperation shown in FIG. 2.

FIG. 5 is a pattern diagram for explaining the selection of the focusdetection area in the AF operation shown in FIGS. 4A and 4B.

FIG. 6 shows a subroutine's flowchart of the image-taking operationshown in FIG. 2.

FIG. 7 shows an example scene in which a one-side blur occurs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the drawings.

FIG. 1A shows the structure of a digital camera 100 as an embodiment ofthe present invention. The digital camera 100 comprises an image-takinglens 101, a diaphragm/shutter 102, an automatic exposure (AE) processor103, a focus lens 104, an automatic focus (AF) processor (driver) 105,an electric flash unit 106, an electric flash (EF) processor 107, animage-pickup element 108, an A/D converter 109, an image processor 110,a white balance (WB) processor 111, a format converter 112, a DRAM 113,a image recorder 114, a system controller 115, a VRAM 116, an operationdisplay 117, operation members 118, an attitude detector 119, a mainswitch 120, a mode switch 121, a first stroke switch (SW1) 122, and asecond stroke switch (SW2) 123.

The image-taking lens 101 includes a zoom mechanism, and makes an objectimage form on the image-pickup element 108. The diaphragm/shutter 102controls a light amount. The AE processor 103 determines an exposureamount automatically based on the luminance of the object. The focuslens 104 forms an in-focus object image on the image-pickup element 108.The focus lens 104 shown in FIG. 1A includes a driving source (steppingmotor, for example), not shown in the figure, and a detector (positiondetector) 104 a that detects the driving amount thereof.

The AF processor 105 has a function of automatic focusing with the TTL(through the lens) technique and the contrast detection method thatdetects a focus state using a high frequency component of a signalshowing the contrast of the object image on the image-pickup element108. The image-pickup element 108 functions as a light-receiving elementor photoelectric conversion element that converts the light reflected bythe object into an electric signal. The A/D converter 109 has a functionto convert analog data into digital data, and includes a correlationdouble sampling (CDS) circuit that eliminates the output noise of theimage-pickup element 108 and a nonlinear amplifier that performsnonlinear amplification of the output of the image-pickup element 108before the A/D conversion.

The image processor 110 performs predetermined pixel interpolationprocessing and color conversion processing for the data from the A/Dconverter 109. Further, the image processor 110 performs predeterminedcalculation processing using taken image data. The system controller 115controls the AE processor 103, AF processor 105 and EF processor 107based on the calculation results. The image processor 110 has anelectronic zoom function converting the input image from theimage-pickup element 108 into a displaying image that is displayed onthe operation display 117.

As described above, the electronic zoom increases the zoom magnificationby enlarging and displaying part of the image signal. In a case wherefurther increase of the magnification is indicated after the zoom lensreached the telephoto end, the electronic zoom increases themagnification by enlarging part of the image signal, thereby achieving ahigher magnification.

The WB processor 111 performs predetermined calculation processing forthe taken image data, and performs AWB (automatic white balance)processing with the TTL technique based on the calculation results forthe taken image data. The format converter 112 converts the format ofthe image data into a predetermined format such as the JPEG format. TheDRAM 113 includes a high-speed built-in memory such as a random accessmemory, and is used as a high-speed buffer to memory the image datatemporarily or a work memory for image compression and decompression.

The image recorder 114 includes a recording medium such as asemiconductor memory, and an interface for the medium. The systemcontroller 115 controls the system in the operation sequence such as theimage-taking sequence, and performs the processes shown in FIGS. 2 to 5.The VRAM 116 functions as an image displaying memory. The operationdisplay 117 displays not only images but also indications for assistingoperations, indications showing the camera status and, at the time ofimage-taking, indications showing the image-taking screen and focusdetection areas. The operation display 117 includes an LCD, LED, speakerand the like.

The operation members 118 are used for operating the camera 100 fromoutside, and include a menu switch for various settings such as asetting of the image-taking function and a setting of image replaying, azoom lever for indicating the zoom operation of the image-taking lens101, an operation mode changing switch for changing the operation modebetween an image-taking mode and a replaying mode, and an electroniczoom ON/OFF switch, for example.

The zoom lever is operated by an user for the zoom operation. The zoomlever can be operated between a telephoto (TELE) position to magnify theimage, a wide-angle (WIDE) position to demagnify the image and an OFFposition. The electronic zoom ON/OFF switch is operated for selectingwhether the electronic zoom is used or not. The electronic zoom can beperformed when the electronic zoom switch is ON, and the electronic zoomcannot be performed when the electronic zoom switch is OFF.

The attitude detector 119 outputs a signal according to the attitude ofthe camera 100 such as an erected attitude (horizontal attitude), aninverted attitude (upside down attitude), a left-sideways attitude(lower grip attitude), a right-sideways attitude (upper grip attitude),an anteverted attitude (lower lens attitude) and a retroverted attitude(upper lens attitude). The system controller 115 can detect the attitudeof the camera 100 based on the signal. Based on the attitude informationdetected by the attitude detector 119, the system controller 115 changesthe weighting for the photometry evaluation and AF, and performsrotation processing of the image taken in the vertical attitude (theleft-sideways attitude or the right-sideways attitude) to display theimage rotated to the vertical position on the operation display 117.

The main switch 120 is a switch for turning on the power of the system.The mode switch 121 is a switch for setting the image-taking mode suchas a program mode, a landscape mode and a portrait mode. The firststroke switch 122 (SW1) is turned on by a half-push operation of arelease switch, not shown in the figure, and is a switch for startingthe image-taking preparation operation such as the AF and the AE. Thesecond stroke switch 123 (SW2) is turned on by a full-push operation ofthe release switch, and is a switch for starting the image-takingoperation (operation for recording the taken image to the recordingmedium).

FIG. 1B shows the arrangement of the focus detection area in the digitalcamera 100 of the present invention. In this figure, reference numeral10 denotes the image-taking screen (field angle area of image-taking).In the image-taking screen 10, nine focus detection areas (image areas)are provided, which include a focus detection area 11 located at thecenter, focus detection areas 12 and 13 located on either side of thecentral focus detection area 11, these focus detection areas 11 to 13constituting the middle area, and include the upper and lower areas eachincluding three focus detection areas (14 to 19).

Hereinafter, the description will be given of the operation of thedigital camera 100 with reference to FIG. 2. FIG. 2 is a flowchart fordescribing the operation of the digital camera 100.

First, the system controller 115 determines whether the main switch 120is turned on or not (step S201). If the main switch 120 is on, thesystem controller 115 determines whether the capacity of the recordingmedium in the image recorder 114 remains or not (step S202). If theremaining capacity is zero, the system controller 115 warns that theremaining capacity is zero (step S203), and returns to the step S201.The warning of the image recorder 114 can be performed by displaying iton the operation display 117 or outputting a warning sound from aspeaker, not shown in the figure. Both of these may be performed.

If the remaining capacity is not zero (step S202), the system controller115 performs the zoom operation (step S204). The description willhereinafter be given of the zoom operation in the step S204 withreference to FIG. 3. FIG. 3 is a flowchart of the subroutine for thezoom operation.

The system controller 115 determines whether the zoom lever included inthe operation members 118 is operated to the TELE position or not (stepS301). If the zoom lever is operated to the TELE position, the systemcontroller 115 determines whether the zoom position of the image-takinglens 101 is located at the TELE end or not (step S302). If the zoomposition is not located at the TELE end, the system controller 115 movesthe zoom position to the TELE end (step S303), and returns to the step301.

On the other hand, if the zoom position is located at the TELE end (stepS302), the system controller 115 determines whether the magnification ofthe electronic zoom by the image processor 110 is set to the maximumvalue or not (step S304). If the magnification of the electronic zoom isnot set to the maximum value, the system controller 115 increases themagnification of the electronic zoom (step S305), and then returns tothe step S301.

On the other hand, if the zoom lever is not operated to the TELEposition (step S301) or the magnification of the electronic zoom is setto the maximum value (step S304), the system controller 115 determineswhether the zoom lever is operated to the WIDE position or not (stepS306). If the zoom lever is operated to the WIDE position, the systemcontroller 115 determines whether the zoom position of the image-takinglens 101 is located at the WIDE end or not (step S307). If the zoomposition is not located at the WIDE end, the system controller 115determines whether the image processor 110 is using the electronic zoomor not (step S308).

If the image processor 110 is using the electronic zoom (step S308), thesystem controller 115 decreases the magnification of the electronic zoom(step S309), and then returns to the step S306. On the other hand, ifthe image processor 110 is not using the electronic zoom (step S308),the system controller 115 moves the zoom position of the image-takinglens 101 to the WIDE side (step S310), and then returns to the stepS306.

If the zoom lever is not operated to the WIDE position (step S306) orthe zoom position of the image-taking lens 101 is located at the WIDEend (step S307), the system controller 115 stores the current zoomposition of the image-taking lens 101 to a calculation memory that isnot shown in the figure and built in the system controller 115 (stepS310).

In FIG. 2, the system controller 115 determines whether the first strokeswitch SW1 is turned on or not after the zoom operation in the step S204(step S205). If the first stroke switch SW1 is off, the systemcontroller 115 determines whether the main switch 120 is on or not (stepS206). If the main switch 120 is on, the system controller 115 returnsto the step S204.

If the main switch 120 is off (step S206), the system controller 115returns to the step S201. On the other hand, if the first stroke switchSW1 is on (step S205), the system controller 115 commands the AEprocessor 103 to perform the AE processing based on the output from theimage processor 110 (step S207).

Next, the system controller 115 performs the AF operation (step S208).The description will hereinafter be given of the AF operation in thestep S208 with reference to FIGS. 4A and 4B. FIGS. 4A and 4B shows aflowchart of the subroutine for the AF operation.

The AF operation is performed by the method in which the focus lens 104is driven between the infinite end and the closest end (hereinafter,this drive is referred to as ‘scanning’), and the position where thevalue of the high frequency component (hereinafter, it is referred to asan AF evaluation value) of the signal from the image-pickup element 108becomes the peak value during the scanning is determined as an in-focuslens position. The scanning of the focus lens 104 is performed for eachof the nine focus detection areas 11 to 19. Different in-focus lenspositions are determined for the focus detection areas corresponding todifferent object distances.

First, the system controller 115 moves the focus lens 104 to a scanningstart position (step S401). The scanning start position is set to theinfinite end in the present embodiment. After starting the scanning, thesystem controller 115 stores the AF evaluation value for each focusdetection area provided in the image-taking screen and the position ofthe focus lens 104 (focus lens position) where each AF evaluation valuehas been obtained to the calculation memory, which is not shown in thefigure and built in the system controller 115 (step S402). The focuslens position can be detected via a detector, not shown in the figure,as a relative position corresponding to the driving amount of thedriving part of the focus lens 104 from a predetermined reset position.

Next, the system controller 115 determines whether or not the focus lensposition is located at the scanning end position (step S403). Thescanning end position is set to the closest end in the presentembodiment. If the focus lens position is not located at the scanningend position (step S403), the system controller 115 moves the focus lens104 in the direction to the closest end by a predetermined amount (stepS404).

If the focus lens position is located at the scanning end position (stepS403), the system controller 115 judges the reliability of the focusdetection result based on the AF evaluation value for each focusdetection area stored in the step S402 and the focus lens position.Further, for the focus detection area with the sufficient reliability,the system controller 115 calculates the focus lens position (in-focuslens position) where the AF evaluation value becomes the peak value(step S405).

The system controller 115 judges the reliability by calculating areliability evaluation value E_(val) using Expression (1), for example.V_(max) and V_(min) denote the maximum and minimum values of the AFevaluation value in a certain focus detection area, and k denotes thenormalization constant. The reliability is judged to be high(hereinafter, it is referred to as ‘O’) if the reliability evaluationvalue E_(val) is equal to 1 or more. The reliability is judged to be low(hereinafter, it is referred to as ‘x’) if the reliability evaluationvalue E_(val) is less than 1. The O-judged focus detection area is afocusable focus detection area (hereinafter, it is referred to as afocusable area).E _(val) =k(V _(max) −V _(min))   (1)

Next, the system controller 115 determines whether the maximum AFevaluation value is obtained at the closest end of the focus lensposition for each focus detection area or not (step S406). If themaximum AF evaluation value is obtained, the system controller 115judges to be ‘Δ’. The Δ-judgment means that any object exists in aregion closer than the scanning region.

Next, the system controller 115 determines whether or not the O-judgedfocus detection area is included in the focus detection areas 11 to 16in the upper or middle area (first screen area) of the image-takingscreen, in a case where, for example, the attitude of the camera 100detected by the attitude detector 119 is the erected attitude (stepS407). If the O-judged focus detection area is included in the upper ormiddle area, the system controller 115 determines whether or not thezoom position of the image-taking lens 101 is located at the positionwhere the measure for the one-side blur should be performed (step S408).This is for preventing the deterioration of the one-side blur at acertain zoom position by the configuration of the image-taking lens 101or the like.

If the zoom position of the image-taking lens 101 is located at theposition where the measure for the one-side blur should be performed,the system controller 115 determines whether or not the central focusdetection area 11 is the O-judged focus detection area and a firstobject distance of the central focus detection area 11, that is, adistance to an object included in the central focus detection area 11,is longer than a first predetermined distance Y as a function of thezoom position (focal length) (step S409).

This is for examining whether or not the image to be taken is a distantview image, which is greatly affected by the one-side blur, and theO-judgment required for performing the focusing has been given to thecentral focus detection area 11. The object distance can be calculatedbased on the detection result of the focus lens position by using therelationship that the object distance becomes longer as the focus lensposition becomes closer to the infinite end and the object distancebecomes shorter as the focus lens position becomes closer to the closestend.

When it is Yes in the step S409, the system controller 115 determineswhether or not a focus detection area in which the object distance isshorter than the first object distance of the central focus detectionarea 11 by a second predetermined distance X or more is included in theO-judged focus detection areas in the upper or middle area (step S410).This is the determination for taking a commemorative photo or the likewith a landscape as the background. In this case, the focus control forthe central focus detection area 11 corresponding to the background isnot performed because pan focus control or focusing on the person isperformed.

Here, the first predetermined distance Y for determining whether or notit is a distant view in the step S409 and the second predetermineddistance X that is a reference of the difference from the objectdistance of the central focus detection area 11 are functions of thezoom position. In other words, these distances are changed according tothe zoom position. This is because the depth of field changes accordingto the zoom position.

If it is NO in the step S410, the system controller 115 selects thecentral focus detection area 11 as a focus target area where thein-focus state is obtained by driving the focus lens 104 (step S411).The system controller 115 drives the focus lens 104 to the position(in-focus position) where the AF evaluation value of the selectedcentral focus detection area 11 became the peak value in the step S405,and thereby achieving the focus control for central focus detection area11 (step S412).

An example of the selection operation of the focus detection area in thesteps S409 and S410 will hereinafter be explained with reference to FIG.5. FIG. 5 is a schematic view for explaining the selection of the focusdetection area, and shows only the central focus detection area 11 shownas ‘C’, the left focus detection area 12 shown as ‘L’, and the rightfocus detection area 13 shown as ‘R’ in the middle area of theimage-taking screen for simplifying the explanation.

In FIG. 5, the object distance A, that is, the distance to the floorlamp S, of the central focus detection area 11 is longer than the firstpredetermined distance Y. When the central focus detection area 11 isthe O-judged focus detection area, the system controller 115 determineswhether or not the left focus detection area 12 in which the objectdistance α (distance to the person P1) is shorter than the objectdistance A by the second predetermined distance X or more, is theO-judged focus detection area.

If the left focus detection area 12 is the O-judged focus detectionarea, the system controller 115 selects the left focus detection area 12as the focus target area, and then drives the focus lens 104 to performthe focus control for the left focus detection area 12.

On the other hand, if the left focus detection area 12 is the x-judgedfocus detection area, since the object distance of the right focusdetection area 13 is not shorter than the object distance A by thesecond predetermined distance X or more (in other words, the objectdistance of the right focus detection area 13 is shorter than the objectdistance A by a distance less than the second predetermined distance X),the system controller 115 selects the central focus detection area 11 asthe focus target area, and then drives the focus lens 104 to perform thefocus control for the central focus detection area 11.

If both the left and right focus detection areas 12 and 13 are theO-judged focus detection areas, and the object distances of the left andright focus detection areas 12 and 13 are shorter than the objectdistance A by the second predetermined distance X or more, the systemcontroller 115 selects the focus detection area having shorter objectdistance of these focus detection areas 12 and 13, that is, theshortest-object-distance focus detection area as the focus target area.

Although the upper and middle areas are the determination object in thesteps S407 and S410 in FIG. 4B, this is only an example. Thedetermination object in the steps S407 and S410 will be changedaccording to the detection result of the attitude detector 119.Accordingly, the determination object in the after-mentioned step S414will be changed from the lower area.

In FIG. 4B, in a case where the zoom position is not a position wherethe measure for the one-side blur should be performed (step S408), in acase where it is NO in the step S409, and in a case where it is YES inthe step S410, the system controller 115 selects, from the O-judgedfocus detection areas in the upper and middle areas, the focus detectionarea in which the in-focus lens position obtained in the step S405corresponds to the closest object distance as the focus target position(step S413).

On the other hand, when no O-judged focus detection area is included inthe focus detection areas 11 to 16 in the upper and middle areas (stepS407), the system controller 115 determines whether or not the O-judgedfocus detection area is included in the focus detection areas 17 to 19in the lower area, according to the camera attitude detected by theattitude detector 119 (step S414).

If the O-judged focus detection area is included in the focus detectionareas 17 to 19 in the lower area, the system controller 115 selects,from the O-judged focus detection areas in the lower areas, the focusdetection area in which the in-focus lens position obtained in the stepS405 corresponds to the closest object distance as the focus targetposition (step S415). Then, the process progresses to the step S412.

On the other hand, if no O-judged focus detection area is included inthe focus detection areas 17 to 19 in the lower area (step S414), thesystem controller 115 determines whether or not the Δ-judged focusdetection area judged in the step S406 is included in the focusdetection areas 17 to 19 in the lower area (step S416). If the Δ-judgedfocus detection area is included in the lower area, the systemcontroller 115 moves the focus lens 104 to the closest end (step S417).Then, the process progresses to the step S412.

If no Δ-judged focus detection area is included in the lower area (stepS416), the system controller 115 determines whether or not thereliability evaluation value E_(val) of the central focus detection area11 obtained in the step S405 is equal to a predetermined value or more(step S418). If the reliability evaluation value E_(val) is equal to thepredetermined value or more, the process progresses to the step S417. Ifthe reliability evaluation value E_(val) is less than the predeterminedvalue, the system controller 115 drives the focus lens 104 to apredetermined position (step S419).

Again, in FIG. 2, the system controller 115 determines whether thesecond stroke switch SW2 is on or not after the AF operation in the stepS208 (step S209). If the second stroke switch SW2 is off, the systemcontroller 115 determines whether the first stroke switch SW1 is on ornot (step S210). If the first stroke switch SW1 is on, the systemcontroller 115 returns to the step S209. If the first stroke switch SW1is off, the system controller 115 returns to the step S204.

If the second stroke switch SW2 is on (step S209), the system controller115 performs the image-taking operation (step S211). The image-takingoperation will hereinafter be explained with reference to FIG. 6. FIG. 6shows a flowchart of the subroutine of the image-taking operation.

First, the system controller 115 measures the object luminance (stepS601). Next, the system controller 115 performs the exposure of theimage-pickup element 108 by controlling the charge storage time and theoperation of the diaphragm/shutter 102 according to the object luminancemeasured in the step S601 (step S602). The object image formed on theimage-pickup element 108 is photoelectrically converted into an analogsignal, and the signal is sent to the A/D converter 109. The A/Dconverter 109 converts the analog signal into a digital signal after thepreprocessing such as the elimination of output noises and the nonlinearprocessing (step S603).

Next, the WB processor 111 adjusts the white balance of the outputsignal from the A/D converter 109 in the image processor 110 to form anadequate output image signal (step S604). Next, the format converter 112converts the output image signal into a predetermined format data suchas the JPEG format data, and then the data is stored to the DRAM 113temporarily (step S605). Next, the data stored in the DRAM 113 istransferred to the image recorder 114, and recorded to the recordingmedium such as a memory in the camera 100 or memory card attached to thecamera 100 (step S606).

Again, in FIG. 2, the system controller 115 determines whether thecapacity of the recording medium in the image recorder 114 remains ornot (step S212). If the remaining capacity of the recording medium iszero, the system controller 115 performs the warning indicating that theremaining capacity is zero (step S213), and then returns to the stepS201.

On the other hand, if the remaining capacity of the recording medium isnot zero (step S212), the system controller 115 determines whether thesecond stroke switch SW2 is on or not (step S213). If the second strokeswitch SW2 is off, the system controller 115 returns to the step S209.If the second stroke switch SW2 is on, the system controller 115 repeatsthe step S213.

As described above, according to the digital camera 100 of the presentembodiment, when taking an image including a distant view such aslandscape in the center area, which is greatly affected by the one-sideblur, the focus control for the focus detection area in which the objectis closer than the object distance of the central focus detection areaby a predetermined distance is performed. Therefore, it is possible toensure the in-focus accuracy for the object corresponding to the focusdetection area provided in an area other than the center of theimage-taking screen. In other words, it is possible to achieve the focuscontrol that the influence of the one-side blur is effectively reduced.

The description was given of the embodiment in which one focus detectionarea is provided at the center of the image-taking screen. However, aplurality of focus detection areas as central focus detection areas maybe provided in a predetermined-sized area including the center, andfurther a plurality of focus detection areas may be provided around thecentral focus detection areas.

This application claims a foreign priority benefit based on JapanesePatent Applications No. 2004-176896, filed on Jun. 15, 2004, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

1. An image-taking apparatus comprising: a focus detector, which detectsthe focus states at a plurality of focus detection areas provided in animage-taking screen; and a selector, which selects a focus target areafrom the plurality of focus detection areas based on the detectionresult of the focus detector, an image-taking lens being focused on anobject in the focus target area, wherein, in a case where a first objectdistance to a first object is longer than a first predetermineddistance, and a second object distance to a second object, which existson an outer side of the first object in the image-taking screen, isshorter than the first object distance by a second predetermineddistance or more, the selector selects the focus detection areacorresponding to the second object as the focus target area.
 2. Theimage-taking apparatus according to claim 1, wherein, in a case wheremore than one second object exists, the selector selects the focusdetection area corresponding to the second object distance shorter thanothers as the focus target area.
 3. The image-taking apparatus accordingto claim 1, wherein, in a case where the first object distance is longerthan the first predetermined distance, and the second object distance isshorter than the first object distance by a distance less than thesecond predetermined distance, the selector selects the focus detectionarea corresponding to the first object as the focus target area.
 4. Theimage-taking apparatus according to claim 1, wherein, in a case wherethe first object distance is shorter than the first predetermineddistance, the selector selects the focus detection area correspondingthe shortest object distance as the focus target area.
 5. Theimage-taking apparatus according to claim 1, wherein the first and thesecond predetermined distances are changed in accordance with the focallength of the image-taking lens.
 6. The image-taking apparatus accordingto claim 1, further comprising a driver, which drives a focus lens sothat the image-taking lens is focused on the object in the focus targetposition.
 7. An image-taking apparatus comprising: a focus detector,which detects the focus states at a plurality of image areas provided inan image-taking screen; and a selector, which selects a focus targetarea from the plurality of image areas based on the detection result ofthe focus detector, an image-taking lens being focused on an object inthe focus target area, wherein, in a case where a first object distanceto a first object displayed in a first screen area of an image-takingscreen is longer than a first predetermined distance, and a secondobject distance to a second object displayed in a second screen area onan outer side of the first object in the image-taking screen, is shorterthan the first object distance by a second predetermined distance ormore, the selector selects the image area corresponding to the secondobject as the focus target area.
 8. The image-taking apparatus accordingto claim 7, wherein, in a case where no focusable area is included inthe first screen area, the selector selects the focus detection areacorresponding to the shortest object distance in the second screen areaas the focus target area.
 9. The image-taking apparatus according toclaim 7, further comprising an attitude detector, which detects theattitude of the image-taking apparatus, and wherein the selector changesthe first and second screen areas in accordance with the detectionresult of the attitude detector.
 10. A focusing method comprising: afocus detection step of detecting the focus states at a plurality offocus detection areas provided in an image-taking screen; and aselection step of selecting a focus target area from the plurality offocus detection areas based on the detection result of the focusdetection step, an image-taking lens being focused on an object in thefocus target area, wherein, in the selection step, in a case where afirst object distance to a first object is longer than a firstpredetermined distance, and a second object distance to a second object,which exists on an outer side of the first object in the image-takingscreen, is shorter than the first object distance by a secondpredetermined distance or more, the focus detection area correspondingto the second object is selected as the focus target area.
 11. Afocusing method comprising: a focus detection step of detecting thefocus states at a plurality of image areas provided in an image-takingscreen; and a selection step of selecting a focus target area from theplurality of image areas based on the detection result of the focusdetection step, an image-taking lens being focused on an object in thefocus target area, wherein, in the selection step, in a case where afirst object distance to a first object displayed in a first screen areaof an image-taking screen is longer than a first predetermined distance,and a second object distance to a second object displayed in a secondscreen area on an outer side of the first object in the image-takingscreen, is shorter than the first object distance by a secondpredetermined distance or more, the image area corresponding to thesecond object is selected as the focus target area.